In such a conventional connector, if mutual directions of the plug and the socket around a center axis of the connector are different when the plug and the socket are connected, there is a possibility that electrical connection relationship of them may be varied or connection pins may be broken. So that, it is desirable that the mutual directions of the plug and the socket around the center axis of the connector at the time of connection always coincide.
In order to make easy positioning around the center axis at the time of connecting such a plug and a socket, a connector that an erroneous insertion prevention key is provided in either one of the plug and the socket (a first connector and a second connector) and the other of them is provided with a spiral extending slope for guiding the erroneous insertion preventing key and a key receiving part connected to the end of the extending slope is known (For example, JP 2010-118224 A)).
Moreover, another connector is known that is, an inclined cam surface and a cam follower are provided on opposing faces of the plug and the socket so as to face each other when the plug and the socket are mutually inserted in the axial direction, and the inclined cam surface and the cam follower are brought into sliding contact with each other, whereby the plug and the socket are relatively rotated and are positioned with respect to each other in the direction of rotation about the center axis. Further, a pin insertion hole is provided at the center of either one of the opposing faces of the plug and the socket, and a center pin protrudes at the center of the other of the opposing faces is provided, and when the plug and the socket are mutually inserted in the axial direction, the center pin is fitted into the pin insertion hole before the inclined cam surface and the cam follower come into contact with each other (For example, US 2017/0062978 A1).